The terminal galactose-α1,3-galactose glycan (herein referred to as Gal-α-Gal) can be a functionally consequential modification to N-glycosylated proteins given its immunogenic potential in humans when presented on heterologously derived biologic therapeutics. The presence of this carbohydrate epitope on endogenous proteins appears to be highly species specific, e.g., detected in pig, mouse, and rat, but absent in primates. Thus, the epitope can be present on recombinant biologics produced in cellular expression systems derived from certain organisms (e.g., Mouse NS0 or SP/2 cells, transgenic pigs). The monoclonal antibody cetuximab (Erbitux®) is one such example of a commercial protein drug product produced in a mouse derived cell line and also reported to contain the Gal-α-Gal carbohydrate epitope (Chung et al. (2008) N Engl J Med 358:1109-1117). The enzymatic biosynthesis of the Gal-α1,3-Gal glycan has been ascribed to 1,3 glycosyl transferase-1 (herein referred to as Ggta1) (Taylor et al. (2003) Glycobiology 13:327-337; Smith et al. (1990) J Biol Chem 265:6225-6234).